In the printing industry where a large amount of organic solvents is used, there has been growing concern about labor and safety, for example, a measure of hydrocarbon emission control regulations in local community, Fire Protection Law and Industrial Safety and Health Law amendment which have recently been enforced in succession. In particular, an aromatic hydrocarbon-based solvent such as benzene, toluene, xylene and the like, which has been preferably used up to now from the aspect of solubility, drying characteristics and the like, is evaporated and diffused into the atmosphere, and is a causative substance which forms an oxidant under photochemical reactions, and therefore strict legal restrictions are imposed on the use the solvent. From these issues, there is an increasing demand for a printing ink with reduced content of an aromatic hydrocarbon solvent. Currently, examples of a non-aromatic solvent, which are being used or which use is considered for a printing ink, include an ester-based solvent such as methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate and the like, a ketone-based solvent such as acetone, methylethylketone and the like, and an alcohol-based solvent such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol and the like.
With respect to a conventional printing ink, resistance to wear, abrasion and scratch of printed products is improved by wax. As such a wax, a polyethylene-based wax is particularly preferable.
Conventionally, in printing ink applications, a polyethylene-based wax has been primarily used in the form of a dispersion or paste prepared by a crystallization method. However, the non-aromatic solvents described above are poor solvents, making it extremely difficult for them to deal with the polyethylene-based wax in these forms. Moreover, a dispersion produced using a wet ball mill and the like has a drawback in that it lacks storage stability because the affinity of the polyethylene-based wax for the above-mentioned non-aromatic solvents is low, and therefore the polyethylene-based wax and the solvent are liable to separate in the dispersion or in the printing ink in which these solvents are used. Furthermore, although the polyethylene-based wax is sometimes used in the form of a fine powder, it is liable to precipitate in the above-mentioned non-aromatic solvents, and likewise it lacks the storage stability of the printing ink in which these solvents are used.